Method of operating a welding power supply and a welding power supply

ABSTRACT

A method of operating a welding power supply during a welding process in which an electric arc between a consumable electrode and a work piece is generated while feeding the consumable electrode and moving the arc in relation to the work piece along a welding track, wherein a transition between a DC power output of the welding power supply and an AC power output of the welding power supply, or vice versa, is made without interruption of the welding process.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/442,898, filed on Feb. 27, 2017, which is a continuation of U.S.patent application Ser. No. 14/115,402, filed on Feb. 6, 2014, now U.S.Pat. No. 9,616,515, which claims priority to international applicationPCT/EP2011/057149, filed on May 4, 2011, the disclosures of all of whichare incorporated herein by reference in their entirety.

FIELD OF THE DISCLOSURE

The present invention relates to a method of operating a welding powersupply. In particular the invention relates to a method of operating awelding power supply which may be set to generate a DC power output ofthe welding power supply as well as an AC power output from the sameoutput terminal. The invention furthermore relates to a welding powersupply which is designed to generate a DC power output of the weldingpower supply as well as an AC power output from the same outputterminal.

BACKGROUND OF THE DISCLOSURE

In welding technology a diversity of welding processes are present.These processes include for example tungsten inert gas welding (TIG),MIG/MAG and submerged arc welding (SAW). In TIG technology an arc isgenerated between a non-consumable electrode and the work piece. Ifdesired a metal filler is fed into the arc. The TIG technology issuitable for welding in thin materials, in particular welding of thinaluminum work pieces. In MIG/MAG and submerged arc welding, an arc isgenerated between a consumable electrode and a work piece. MIG/MAG issuitable for welding of all kinds of metals at medium thickness. In TIGand MIG/MAG welding a weld puddle generated by the arc is protected by agas supplied from a shield cup arranged at a welding torch. In submergedarc welding (SAW) an arc is generated between a consumable electrode anda work piece under a protective layer of flux covering the work piece atthe arc. MIG/MAG is suitable for welding of all kinds of metals wherehigh deposition rates are required, such as when welding in thickmaterials.

In the field of welding different parameters may be adjusted to achievea desired result. These parameters includes welding voltage, weldingcurrent, electrode feed speed and welding propagation speed.

Furthermore, welding processes may be performed by a direct currentprocess with an output from the power source connecting the electrode tothe negative potential, a direct current process with an output from thepower source connecting the electrode to the positive potential or as analternating current process where the electrode switches betweenelectrode negative and electrode positive. Generally electrode negativeprovides for a wide weld bead with low penetration and electrodepositive provides for a narrow bead with deep penetration. Thealternating current process can be seen as a process having propertiesin between the DC-negative and DC-positive process. Generally thealternating current has a base frequency of around the net frequency.Optionally, the frequency can be higher, that is the region of 200-400Hz. High frequencies will generate losses in welding cables and istherefore not suitable for many applications.

Welding power sources that may operate in either DC mode or AC mode arepreviously known. One example is disclosed in U.S. Pat. No. 4,517,439where separate AC and DC terminals are provided.

Even though the prior art is rich when it concerns improvements incontrol of the welding power supplies to generate weld seams with highquality, it is desirable to provide further improved methods foroperating welding power supplies.

It is thus an object of the present invention to provide an improvedmethod of operating a welding power supply during a welding process.

SUMMARY

The object of further improving a welding process is achieved by amethod of operating a welding power supply during a welding processaccording to claim 1.

According to the inventive method an electric arc between a consumableelectrode and a work piece is generated while feeding a consumableelectrode and moving the arc in relation to the work piece along awelding track. During the welding process a transition is made between aDC power output of the welding power supply and an AC power output ofthe welding power supply, or vice versa. Hence according to theinvention the transition between a DC power output and an AC poweroutput, or vice versa, is made without interruption of the weldingprocess.

By, as is proposed by the inventive method, allowing a transitionbetween AC and DC output during a welding process while feeding aconsumable electrode and moving the arc in relation to the work piecealong a welding track it is possible to adapt the weld process torapidly changing welding conditions such as a transition between a rootrun and a following hot pass. When performing a root run a deeppenetration is required in order to make a fully dense joint between twoopposing end portions facing each other with a narrow gap in between. Byoperating the power supply to provide a DC-positive output deeppenetration is ascertained. When the root run is completed it is oftendesirable to complete the weld seam by providing hot pass followed byone or more fill passes. In such circumstances the invention proposes toperform a shift to an AC process for a provision of one or more fillerruns from a DC-positive electrode process completing the root runwithout interrupting the welding process. This means that the feeding ofthe consumable electrode as well as movement of the arc in relation tothe work piece will continue at the transition. By avoiding interruptingthe process it can be assured that the weld puddle is not solidified orcooled. Hence, fusion defects can be avoided at the location of thetransition between the end of the root run and the beginning of thefiller strings. According to prior art methods, chamfering may be neededin order to avoid possible fusion defects at the location of the startof the AC process following after the root run. By using the methodaccording to the invention a time consuming chamfering process is beavoided.

A further advantage of the inventive process is that effective arc blowprevention may be performed at welding tracks having complex geometry,where arc blow occurs at an unacceptable level at certain segments ofthe weld track, while the arc blow is on a low level at other segmentsof the weld track. In such situations, a transition between a DC poweroutput of the welding power supply and an AC power output of the weldingpower supply or vice versa may be made in dependence of the specific arcblow condition at the location. A DC power output may be used in thesegments where the arc blow is low due to geometry and a transition toan AC process can be made without interruptions at segments where thegeometry induces large arc blow. By allowing the transition to takeplace, the benefits of the DC process can be used for certain segmentswhile a reduction of the arc blow due to the use of an AC process forother segments is allowed without interruption of the welding process.

It is therefore contemplated to optionally perform an assessment of aparameter representing arc blow at a welding location and to adjust abalance in dependence of the assessed parameter value.

At the transition between the AC and DC processes, the welding speed andthe electrode feed speed may be maintained. This means thatv_(DC)(t0)=v_(AC)(t0), where v_(DC)(t0) is the welding speed of the DCprocess at the time of transition t0 and v_(AC)(t0) is the welding speedof the AC process at the time of transition. Similarly,w_(DC)(t0)=w_(AC)(t0), where v_(DC)(t0) is the electrode feed speed ofthe DC process at the time of transition t0 and v_(AC)(t0) is theelectrode feed speed of the AC process at the time of transition.Optionally, the electrode feed speed and the welding speed at steadystate may be different from the electrode feed speed respectively thewelding speed at the transition. This means that v_(DC)(ts)≠v_(DC)(t0)for ts≠t0, where ts are the time at which the process is run at steadystate. Further, v_(AC)(ts)≠v_(AC)(t0) for ts≠t0, w_(DC)(ts)≠w_(DC)(t0)and w_(AC)(ts)≠w_(AC)(t0). The transition between the AC and DCprocesses can be smoothened by allowing ramps of the electrode feedspeed at the transition. In the event the location of a discontinuity atwhich the process should change from AC to DC is known prior to arrivingat the discontinuity, the ramp can be distributed on both sides of thetransition

In order to generate a suitable weld an AC balance value may be set inorder to provide an appropriate penetration value for a weld process tobe performed. The AC balance is a ratio between the electrode positiveand electrode negative. The AC balance B is defined as proportion ofelectrode positive during a weld cycle. A balance of 100% DC positivehas no DC negative component in a weld cycle. A balance of 0% DCpositive has no DC positive component in a weld cycle. In an embodimentof the invention, a balance between positive electrode potential andnegative electrode potential during a welding cycle is thus continuouslyadjustable between DC-negative electrode and DC-positive electrode viathe AC power output. By allowing a continuously adjustable balancebetween 0 and 100% DC-positive electrode at an AC process, the characterof the arc can be suitable adapted to the welding conditions.

In one embodiment of the invention, it is therefore suggested to assessa surface profile of the weld bead at a welding location and adjust thebalance in dependence of the surface profile at the welding location.The assessment may be based on a predefined map including information ofa surface profile as a function of the welding location. The surfaceprofile is the geometry of the weld track at the welding location. Inthe assessment, a desired welding penetration profile may be retrievedfor the welding location where after the balance may be set independence of the desired welding penetration profile at the location.

The assessment may include determining of a current welding location andretrieving a value representing the desired balance at the currentwelding location.

Optionally a sensor may be used to determine a surface profile of thewelding track at the welding location and the balance may be set inaccordance with the detected surface profile.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will be described in further detail belowwith reference to appended drawings, where:

FIG. 1 shows a schematic drawing of a welding arrangement according tothe invention,

FIG. 2 shows a schematic drawing of a pipe welding process,

FIG. 3 shows a schematic drawing of a weld seam including a root portionat an area where a transition from an uncompleted root run to acompleted root run is located,

FIG. 3a shows a symbolic drawing of a weld track having a surfaceprofile with a wedge portion and a root portion,

FIG. 4 shows a diagram of a weld depth as a function of the positionalong a weld track,

FIG. 5 shows a diagram with a desired balance as a function of thewelding location,

FIG. 6 shows a schematic map of a welding process along a track, and

FIG. 7 shows a schematic flowchart of an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a welding arrangement 10 suitable for use in a methodaccording to the invention. The welding arrangement includes a weldingpower source 20 capable of operating in DC mode as well as AC mode. Thewelding power supply is suitably an inverter power source which may beof a design as presented in U.S. Pat. No. 5,710,696. The power sourceincludes a DC stage 30 connected to an AC input 31 and a DC output 32.The DC stage 30 includes a transformer stage 33 which generates a lowvoltage high current output to a rectifier stage 34, which may bedesigned by a diode bridge and a capacitor. The output from therectifier stage is provided to a switching regulator 35 includingswitches which provides a chopped DC output signal of the output fromthe rectifier circuit. The chopping frequency is generally around 10-25kHz.

The output from the switching regulator 35 is fed to an AC stage 40formed by an inverter circuit 41. The inverter circuit 41 includes a setof switches 42 enabling transformation from the DC input to an AC outputin a conventional manner as disclosed in U.S. Pat. No. 5,710,696. Whenoperating in DC mode the inverter circuit 41 is controlled to provide aconstant polarity DC output. This is performed by not switching betweenthe states of the switches 42. When operating in DC mode, either a DCnegative output or a DC positive output may be provided depending on theselected control of the switches 42.

A control arrangement 50 is arranged to control the output of thewelding power supply 20. The control arrangement includes a digitalsignal processor 51. The digital signal processor 51 serves to controlthe shape of current pulses by controlling the switches of the switchingregulator 35. For this purpose the digital signal processor 51 mayinclude a pulse width modulator under control of a wave shaper locatedin a general controller 54. The control of the switches may be performedin a manner as disclosed in U.S. Pat. No. 5,715,150.

The digital signal processor 51 receives as input signals current andvoltage output values detected by sensors 52, 53 at the output from theinverter 41 or from the switching regulator 35. Furthermore the generalcontroller 54 determines desired values of the welding voltage V,welding current I, electrode feed speed, w, and welding speed v. Thesevalues may be set by an operator from an operator interface 55, or froma map 56 containing preset welding parameters depending on selected weldcases.

The digital signal processor 51 is furthermore responsible forcontrolling the balance of an AC output from the inverter circuit 41, ifprovided. This control is performed by setting switching times of theswitches 42.

Optionally the controller receives an input from a welding profilesensor 61, which determines the profile of a surface at a weldinglocation. The welding profile sensor may determine a desired weldpenetration that is a welding depth at the welding location. The weldingdepth may be defined as a distance between a highest and lowest pointwithin a welding area, where the welding area corresponds to a weldpuddle at the welding location. Since welding may be performed with awork piece inclined at any desired angle with respect to the verticalplane, the depth is measured in the direction between the arc and thepoint of the weld puddle having the deepest penetration. In the case ofa weld performed in the vertical plane, the depth will be measured inthe vertical plane. In the root run the depth will correspond to thethickness of the root, while at the filler rounds the depth will dependon the weld profile.

Instead or complementary to the weld profile sensor 61, a weld profilemap 63 may be provided. The weld profile map includes data representinga desired welding depth or a desired balance as a function of thewelding location or a combination thereof. Expressed in weldingcoordinates s, where s is a location along a welding track the map maybe expressed as B(s) where B is the balance at a desired locationproviding a desired welding penetration D at a location s along awelding track. Alternatively the map may be expressed as D(s), whereD(s) is a desired penetration at a location s along a welding track. Inthis event, a map between a desired balance and a desired weldingpenetration profile should be provided. The map 63 between a desiredwelding penetration profile D and a desired balance value may be storedin a memory area 64 accessible for the general controller 54. The map 63is created from experimental results from different weld cases.

Optionally a ramp controller 65 is connected to the general controller54. The ramp controller controls the process parameters welding voltageV, welding current I, electrode feed speed, w, and welding speed v at adetected discontinuity along the welding track.

The welding arrangement further includes a welding robot 70 including atleast one welding head 71 through which a consumable electrode 72 isfed. The welding robot 71 further includes an electrode feeder 73arranged to feed the welding consumable electrode 72 at a desiredelectrode feed speed w. The welding arrangement includes a propulsionunit arranged to generate a relative movement between the work piece andthe welding head. The propulsion unit may be provided by a movablewelding robot, which may propagate in relation to the work piece or byarranging the work piece to be movable. In FIG. 1, the welding robot 70is movable, while in FIG. 2, which shows an arrangement for pipe weldingincluding a pipe support 81 on which a pipe 82 is located. A fixedwelding head 83 is arranged to provide an arc at a specified location.The pipe support 81 includes one or more driven rollers which rotatesthe pipe.

FIG. 3 shows a schematic drawing of a weld seam 90 including a rootportion 91 and a wedge portion 92 of a work piece 102. The root portionshould be welded in a root run providing a complete root weld. Thewelding is preformed along a welding track 103. A welding head 93 guidesa consumable electrode 94 at which an arc 95 is formed. The schematicdrawing shows an area 96 where a transition 97 from an uncompleted rootrun 99 to a completed root run 98 is located. The welding is performedin the direction indicated by the arrow 100. At a current weldinglocation S(t) welding is performed at an open root. At the locationS(t₀) a transition is made to a location where a completed root ispresent. Welding should here be continued in the wedge portion bysupplying filler strings.

In FIG. 3a a symbolic drawing of a surface profile 301 having with awedge portion 92 and a root portion 91 is shown. The surface profile maycontain information about both the wedge portion, which is to be weldedin a later subsequent run or subsequent runs, and the root portion whichis to be welded in an initial run. That is the surface profile 301 maycontain information relating to the ongoing and coming welding runs.Alternatively the surface profile only contains information relating tothe coming run. The surface profile may contain information relating tothe depth and width of the gap which is to be joined. A complete surfaceprofile as exemplified in FIG. 3a may contain information regarding thedepth of the root d_(r), the width of the root w_(r), the wedge portiond_(w), and the width of the wedge portion w_(w). In FIG. 3a a rootstring 303 formed during a root pass and filler strings 305, 307, 309formed during subsequent passes are shown.

When performing a root run a deep penetration is required in order tomake a fully dense joint between two opposing end portions facing eachother with a narrow gap in between. By operating the power supply toprovide a DC-positive output deep penetration is ascertained. When theroot run is completed it is often desirable to complete the weld seam byproviding one or more filler strings on top of the root run. In suchcircumstances the invention proposes to perform a shift to an AC processfor a provision of one or more filler runs from a DC-positive electrodeprocess completing the root run without interrupting the weldingprocess. This means that the feeding of the consumable electrode as wellas movement of the arc in relation to the work piece will continue atthe transition. By avoiding interrupting the process it can be assuredthat the weld puddle 101 is not solidified or cooled. Hence, fusiondefects can be avoided at the location of the transition between the endof the root run and the beginning of the filler strings. According toprior art methods, chamfering may be needed in order to avoid possiblefusion defects at the location of the start of the AC process followingafter the root run. By using the method according to the invention atime consuming chamfering process may be avoided.

At the transition between the DC and AC processes, the welding speed andthe electrode feed speed is maintained. The transition takes place atthe location to where the discontinuity from the root run to the fillerrun is located. This means that v_(DC)(t0)=v_(AC)(t0), where v_(DC)(t0)is the welding speed of the DC process at the time of transition to andv_(AC)(t0) is the welding speed of the AC process at the time oftransition. Similarly, w_(DC)(t0)=w_(AC)(t0), where w_(DC)(t0) is theelectrode feed speed of the DC process at the time of transition to andw_(AC)(t0) is the electrode feed speed of the AC process at the time oftransition. Optionally, the electrode feed speed and the welding speedat steady state may be different from the electrode feed speed and thewelding speed, respectively, at the transition. This means thatv_(DC)(ts)≠D_(DC)(t0) for ts≠t0, where ts are the time at which theprocess is run at steady state. Further, v_(AC)(ts)≠A_(AC)(t0) forts≠t0, w_(DC)(ts)≠w_(DC)(t0) and w_(AC)(ts)≠w_(AC)(t0). The transitionbetween the AC and DC processes can be smoothened by allowing ramps ofthe electrode feed speed at the transition. In the event the location ofa discontinuity at which the process should change from AC to DC isknown prior to arriving at the discontinuity, the ramp can bedistributed on both sides of the transition.

In FIG. 4 a desired welding penetration profile as a function of alocation along a welding track is disclosed. At the location to where adiscontinuity between a root run and a filler run is present. Thedesired welding penetration profile D falls at this location from a highvalue corresponding to a DC-positive output power mode to a lower valuecorresponding to an AC output having a certain balance B.

A corresponding diagram with a desired balance B as a function of thewelding location is disclosed in FIG. 5. The transition 503 from theDC-positive output power mode 501 to the AC output power mode 502 maycontain a ramp continuing over several AC pulses or be performed in asingle pulse, where the process is changed from a steady stateDC-positive process to a steady state AC process having a certainbalance value via a transition phase with a change of the balance valueover the several pulses. This is indicated by the smooth portion betweenthe DC-positive process and the steady state AC process occurring aftert₀+Δ.

Effective arc blow prevention may be performed at welding tracks havingcomplex geometry, where arc blow occurs at an unacceptable level atcertain segments of the weld track, while the arc blow is acceptable atother segments of the weld track. Here a transition between a DC poweroutput of the welding power supply and an AC power output of the weldingpower supply, or vice versa, in dependence of the specific arc blowcondition at the location. A DC power output may be used in the segmentswhere the arc blow is low due to geometry and a transition to an ACprocess can be made without interruptions at segments where the geometryinduces large arc blow. By allowing the transition to take place, thebenefits of the DC process can be used for certain segments while areduction of the arc blow due to the use of an AC process for othersegments is allowed without interruption of the welding process.

It is therefore contemplated to optionally perform an assessment of aparameter representing arc blow at a welding location and to adjust abalance in dependence of the assessed parameter value. This may bepossible by either detecting an arc blow condition and changing theoutput power from DC to AC where arc blow is detected or by providing amap over the desired welding condition as a function of the positionalong a welding track, where at locations sensitive to arc blow atransition from DC output to AC output is made without interrupting thewelding process.

In FIG. 6 a schematic map of a welding process along a track definedalong a coordinate S is indicated. The map includes two areas A1 and A2where a DC-positive process is run and three areas A3, A4, A5 withdifferent balance values are performed.

In FIG. 7 a schematic flowchart of an embodiment of the invention isshown. In a first process step S10 an AC or DC output power process isrun at an electrode feed speed w and a welding speed v. At a step S20 itis determined whether a discontinuity is present, such as a transitionfrom a root run to a filler run or from an acceptable arc blow conditionto an unacceptable arc blow condition takes place. The discontinuity canbe detected by sensors or by a map indicating a discontinuity. If adiscontinuity is present, the process will in a step S30 change from DCto AC or vice versa depending on the nature of the discontinuity. If adiscontinuity is not present, the process will return to step S10 if thecurrent process is a DC process (Yes at step S40). If the currentprocess is an AC process, the balance value may be determined in aprocess step S50. The desired balance value may be obtained from a map63.

The welding process may include a root pass and one or more fill passes,wherein said root pass is made with a DC-positive electrode. The fillpasses are made with an AC power output, and that a transition betweenthe DC-positive electrode and the AC power output is made withoutinterruption of the welding process.

The welding process may thus include the steps of performing a root passwith a DC-positive electrode, determining that the root pass iscompleted, and switching to an AC power output when said root pass iscompleted without interrupting the welding process.

The process allows for an adjustable balance between negative electrodepotential and positive electrode potential during a welding cycle, whichbalance may be continuously adjustable between DC-negative electrode andDC-positive electrode via the AC power output.

In a step S60 a surface profile of the welding track at a weldinglocation is assessed and that the balance is adjusted in dependence ofthe surface profile at the welding location. In one embodiment theassessment is based on retrieving a desired welding penetration profileat the welding location and setting the balance in dependence of thedesired welding penetration profile at the location. Optionally theassessment is based on a predefined map including information of thesurface profile as a function of the welding location.

Optionally assessment includes determining of a current welding locationand retrieving a value representing the desired balance at the currentwelding location. Optionally a sensor determines a surface profile ofthe welding track at the welding location.

The foregoing description is provided to illustrate and explain thepresent invention. However, the description hereinabove should not beconsidered to limit the scope of the invention set forth in the claimsappended here to.

What is claimed is:
 1. A method, comprising: receiving informationincluding data representing at least a welding depth in a weldingprocess on a work piece; and based on the information: performing afirst transition from a DC power mode of a welding power supply to an ACpower mode of the welding power supply; and performing a secondtransition from the AC power mode of the welding power supply to the DCpower mode of the welding power supply, wherein the first transition andthe second transition are performed without interruption of the weldingprocess, and wherein the first transition and the second transition areperformed without interruption including moving an electric arc on thework piece at a constant speed at the first transition and the secondtransition.
 2. The method according to claim 1, wherein the weldingprocess includes generating the electric arc between a consumableelectrode and the work piece.
 3. The method according to claim 1,further comprising providing a continuously adjustable balance between anegative electrode potential and a positive electrode potential duringthe welding process.
 4. The method according to claim 3, wherein thecontinuously adjustable balance between the negative electrode potentialand the positive electrode potential is between a DC-negative electrodeand a DC-positive electrode.
 5. The method according to claim 1, whereinthe information is included in profile information including at least aweld profile map, the weld profile map including data representing aweld depth to be applied to the work piece.
 6. The method according toclaim 1, wherein the information comprises information from a sensor,the information from the sensor including a surface profile of a weldingtrack at a welding location.
 7. An apparatus, comprising: a weldingpower source configured to operate in a DC power mode and an AC powermode; a memory storing information including data representing at leasta welding depth in a welding process on a work piece; and a processorconfigured, based on the information, to: perform a first transitionfrom the DC power mode and the AC power mode; and perform a secondtransition between the AC power mode and the DC power mode, wherein theprocessor is further configured to cause the first transition and thesecond transition to be performed without interruption of the weldingprocess while moving an electric arc on the work piece at a constantspeed at the first transition and the second transition.
 8. Theapparatus according to claim 7, wherein the welding process includesgenerating the electric arc between a consumable electrode and the workpiece.
 9. The apparatus according to claim 7, wherein the consumableelectrode provides a continuously adjustable balance between a negativeelectrode potential and a positive electrode potential during thewelding process.
 10. The apparatus according to claim 9, wherein thecontinuously adjustable balance between the negative electrode potentialand the positive electrode potential is between a DC-negative electrodeand a DC-positive electrode.
 11. The apparatus according to claim 7,wherein the information is included in profile information including atleast a weld profile map, the weld profile map including datarepresenting a weld depth to be applied to the work piece.
 12. Theapparatus according to claim 7, further comprising a sensor to providethe information stored in the memory.
 13. The apparatus according toclaim 12, wherein the information from the sensor includes a surfaceprofile of a welding track at a welding location.
 14. A method,comprising: performing a root weld on a work piece using a DC modeassociated with a welding power source; performing a filler weld on thework piece using an AC mode associated with the welding power source;and transitioning from the root weld to the filler weld withoutinterrupting operation of the welding power source while moving anelectric arc on the work piece at a constant speed at the transitionfrom the root weld to the filler weld.
 15. The method according to claim14, further comprising providing a continuously adjustable balancebetween a negative electrode potential and a positive electrodepotential during the welding process.
 16. The method according to claim14, further comprising generating the electric arc with a consumableelectrode to perform the root weld and the filler weld.
 17. The methodaccording to claim 14, wherein performing the root weld on the workpiece occurs prior to performing the filler weld on the work piece. 18.The method according to claim 14, further comprising providing weldingprofile information that includes at least a welding penetration depththat is to be achieved by the root weld.
 19. The method according toclaim 18, wherein the welding profile information includes a weldingcoordinate corresponding to the welding penetration depth.
 20. Themethod according to claim 14, wherein performing the filler weld on thework piece includes applying the filler weld over the root weld.